The present invention relates to fluid flow control valves and, more particularly, to a butterfly valve which is corrosion resistant and provides high purity service in high purity fluid media systems.
Butterfly valves are widely used in fluid media systems to regulate flow. Butterfly valves comprise a body, a stem, and a disk member pivotally movable in the fluid media passage defined by the valve body and an annular seat. The annular seat forms a fluid seal with the disk member in the closed position of the valve.
Butterfly valves are commonly used in aggressive fluid media systems that place severe demands on the valve materials. Applications for these valves include, for example, high purity fluid media systems such as high purity, de-ionized water systems in the semiconductor industry, and fluid systems in the food industry, and highly corrosive chemical systems. Such fluids are extremely corrosive to non-specialty metals. Accordingly, butterfly valve components have been formed of specialty metals such as stainless steels and titanium in an effort to provide enhanced corrosion resistance. These metals have also proven to be inadequate, however, as they also can corrode when used, for example, in high purity, de-ionized water systems.
The wetted metallic components of the known butterfly valves have also been coated with materials such as PTFE to provide chemical resistance. Although these coatings are chemically resistant, they can fail during operation and expose the underlying metal to corrosive attack. As a result, the failed coating and the corrosion product can contaminate the fluid media.
The known butterfly valves have also included non-metallic, non-coated components. For example, plastic valve bodies, elastomeric valve seats, and elastomeric O-ring seals on the disk member or the valve seat, are commonly incorporated into butterfly valves. These components have proved not to be satisfactory because many plastic and elastomeric materials are unable to provide prolonged, non-contaminating service in high purity, highly aggressive fluid media such as high purity, de-ionized water. Some plastics, including PVC and CPVC, contain constituents such as carbon that can be leached out by high purity fluid media and contaminate the fluid media systems. The elastomeric components deteriorate and allow fluid media to leak into various areas of the valve and corrode, or cause leaching of, the metal components. The elastomeric materials can then become entrained in the fluid media stream and contaminate the system.
Furthermore, known butterfly valves typically comprise joints, seams, crevices and grooves in the fluid media passage at which stagnation and contamination can occur.
Another problem is that the known butterfly valves are designed to contain fluid media leakage within the valve body. The valve bodies either have a one-piece body or comprise two body halves. In the one-piece body construction, sealing elements are typically provided about the stem to contain the fluid media inside the body. In the two-piece body constructions, a seal is typically positioned between the body halves to prevent any fluid media that leaks into the valve stem area from passing out of the valve body. The contained fluid can corrode, or cause leaching of, metal components of the valve, and the resultant contamination can become entrained in the fluid media stream.
Moreover, because the leaked fluid media is contained within the body in the known butterfly valves, it is not possible to visually examine the outer surface of the valves for evidence of internal fluid media leakage. As a result, when contamination is detected in the system, it is not possible to simply visually inspect each of the valves to positively locate the contamination source. This problem has severe implications in multi-valve systems. In order to determine the source of contamination in such systems, it is necessary to shut down the system and disassemble a number of valves to locate a faulty valve. After the faulty valve is repaired or replaced, the system can then be re-activated. If contamination is determined to still be present in the system, however, the system must be shut down once again and additional valves must be disassembled and inspected to positively eliminate the source of contamination. Such system shut-down and valve disassembly and inspection can result in significant lost service time and related costs.
Thus, there is a need for an improved butterfly valve that overcomes the above-described problems associated with the known butterfly valves and provides contamination free service in high purity fluid systems. More particularly, there is a need for a butterfly valve that i) is resistant to corrosive fluid media and all wetted components are substantially not subject to leaching; ii) comprises no coated wetted components to contaminate the system in the event of coating failure; iii) comprises no wetted elastomeric elements that can deteriorate and contaminate the system; iv) provides a direct interference seal between the disk member and the seat without the use of wetted elastomeric seals; and v) allows leaked fluid media to pass out of the body to prevent potential contamination of the fluid media stream and to enable external visual inspection of the butterfly valve for internal fluid leakage.